Hoping someone can help me with this one. I am having a bit of trouble with my heater system. I have good heat but can't get heat to upper defrost. I took apart the lower venting and the door to direct heat up does not open. I can manually open it but it will not on its own. I see that it is operated by a vacuum system but I can't seem to find any trouble with the lines(holes). I am thinking maybe a line is off that controls the heater diaphram or the unit is dead. The lines that go to the control levers all seem to be there and functioning. Where does the line to the diaphram go to to get the vacuum? I can't seem to find it without taking the whole darn thing apart. Or, do I need a new one?